High efficiency light-emitting diode and method for manufacturing the same

ABSTRACT

A high efficiency light-emitting diode and a method for manufacturing the same are described. The high efficiency light-emitting diode comprises: a permanent substrate; a first contact metal layer and a second contact metal layer respectively deposed on two opposite surfaces of the permanent substrate; a bonding layer deposed on the second contact metal layer; a diffusion barrier layer deposed on the bonding layer, wherein the permanent substrate, the bonding layer and the diffusion barrier layer are electrically conductive; a reflective metal layer deposed on the diffusion barrier layer; a transparent conductive oxide layer deposed on the reflective metal layer; an illuminant epitaxial structure deposed on the transparent conductive oxide layer, wherein the illuminant epitaxial structure includes a first surface and a second surface opposite to the first surface; and a second conductivity type compound electrode pad deposed on the second surface of the illuminant epitaxial structure.

RELATED APPLICATIONS

This application is a continuation application of, and claims priorityfrom, U.S. patent application Ser. No. 11/687,874, filed Mar. 19, 2007now U.S. Pat. No. 7,811,838, which is based on, and claims priorityfrom, Taiwan Application Serial Number 95150033, filed Dec. 29, 2006,the disclosure of which is hereby incorporated by reference herein inits entirety.

FIELD OF THE INVENTION

The present invention relates to a light-emitting diode (LED) and amethod for manufacturing the same, and more particularly, to a highefficiency light-emitting diode and a method for manufacturing the same.

BACKGROUND OF THE INVENTION

In the fabrication of light-emitting diodes, group III-V compoundsemiconductors, such as GaP, GaAsP, GaInP, AlGaAs, AlGaP and AlGaInP,are common. Typically, a material of a growth substrate of aconventional light-emitting diode adopts N-type gallium arsenide (GaAs).The growth substrate composed of N-type GaAs can absorb light, so thatmost of the photons produced by the active layer of the light-emittingdiode while being emitted towards the growth substrate are absorbed bythe growth substrate, thus seriously affecting the light emittingefficiency of the light-emitting diode device.

In order to prevent light being absorbed by the substrate, a method thatdirectly bonds the GaAs light-emitting diode wafer to the silicon (Si)substrate after the GaAs light-emitting diode wafer is stripped off theGaAs substrate has been developed. Additionally, the U.S. Pat. No.5,376,580 (application date: Mar. 19, 1993) filed by Hewlett-PackardCo., U.S.A. disclosed a technology about directly bonding the AlGaAslight-emitting diode wafer to the other substrate after the AlGaAslight-emitting diode wafer is stripped off the GaAs substrate. However,the disadvantages of the U.S. Pat. No. 5,376,580 include processingdifficulties and low yields caused by the need to consider theconsistency of the lattice direction between the bonding wafers, sincethe bonding mediums are semiconductors.

In the conventional bonding process, a bonding step has to be performedfirst, and processes of an illuminant epitaxial structure and apermanent substrate are performed, so that the bonding temperature islimited to a value larger than the process temperature of the illuminantepitaxial structure. Under higher bonding temperature, the material ofan adhesive layer must adopt materials with higher melting points andlarger hardness, so that degradation in the operating of thelight-emitting diode easily occurs.

Further, in order to improve the current-spreading effect of alight-emitting diode, a typical design is to increase the area ofelectrodes. However, the electrodes are opaque, so that increasing ofthe area of the electrodes results in increasing the opaque area,thereby decreasing brightness of the light-emitting diode.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide a high efficiencylight-emitting diode, in which no high temperature process is performedafter the bonding of an illuminant epitaxial structure and a permanentsubstrate, so that the selectiveness of the bonding material isincreased, thereby providing easier process conditions, broadening theprocess window of the bonding process and effectively enhancing thereliability of the light-emitting diode.

Another aspect of the present invention is to provide a high efficiencylight-emitting diode, which has a P-side up illuminant epitaxialstructure, so that a transparent current-spreading layer with a largerthickness and higher electrical conductivity can be epitaxially grown.Accordingly, light extraction efficiency is increased, thecurrent-spreading effect is improved, and the area of the opaqueelectrodes is decreased, thereby enhancing brightness of thelight-emitting diode.

Still another aspect of the present invention is to provide a highefficiency light-emitting diode, in which silicon may be adopted as amaterial of a permanent substrate. Because silicon has properties ofhigh thermal conductivity, high electrical conductivity, being easilyprocessed, and superior reliability operated under large current,operation performance of the light-emitting diode is effectivelyenhanced.

Yet another aspect of the present invention is to provide a method formanufacturing a high efficiency light-emitting diode, which can provideeasier process conductions, so that reliability of the light-emittingdiode is further enhanced.

According to the aforementioned aspects, the present invention providesa high efficiency light-emitting diode, comprising: a permanentsubstrate including a first surface and a second surface on oppositesides, wherein the permanent substrate is electrically conductive; afirst contact metal layer and a second contact metal layer respectivelydeposed on the first surface and the second surface of the permanentsubstrate; a bonding layer deposed on the second contact metal layer,wherein the bonding layer is electrically conductive; a reflectivecontact structure deposed on the bonding layer; an illuminant epitaxialstructure deposed on the reflective contact structure, wherein theilluminant epitaxial structure includes a first surface and a secondsurface on opposite sides, the illuminant epitaxial structure comprisesa first conductivity type cladding layer, an active layer, a secondconductivity type cladding layer and a transparent current-spreadinglayer stacked in sequence, and the first conductivity type claddinglayer and the second conductivity type cladding layer are differentconductivity types; and a second conductivity type compound electrodepad deposed on a portion of the second surface of the illuminantepitaxial structure.

According to a preferred embodiment of the present invention, thebonding layer is composed of an adhesive layer, and a material of theadhesive layer is preferably PbSn, AuGe, AuBe, AuSn, Sn, In or PdIn.According to another preferred embodiment of the present invention, amaterial of the permanent substrate is preferably Si, Ge, SiC, AlN, Cuor Al for electrical conduction.

According to the aforementioned aspects, the present invention furtherprovides a method for manufacturing a high efficiency light-emittingdiode, comprising: providing a growth substrate; forming an etching stoplayer on the growth substrate; forming a first conductivity type ohmiccontact layer on the etching stop layer; forming an illuminant epitaxialstructure on a surface of the first conductivity type ohmic contactlayer, wherein the illuminant epitaxial structure includes a firstsurface and a second surface on opposite sides, and the first surface ofthe illuminant epitaxial structure is directly connected with thesurface of the first conductivity type ohmic contact layer; forming asecond conductivity type compound electrode pad on a portion of thesecond surface of the illuminant epitaxial structure; providing atemporary substrate; bonding the temporary substrate to the illuminantepitaxial structure and the second conductivity type compound electrodepad by using a first bonding layer, wherein the first bonding layer issandwiched in between the temporary substrate and the second surface ofthe illuminant epitaxial structure; removing the growth substrate toexpose the etching stop layer; removing the etching stop layer to exposethe first conductivity type ohmic contact layer; providing a permanentsubstrate; bonding the permanent substrate to the exposed firstconductivity type ohmic contact layer by using a second bonding layer,wherein the second bonding layer is sandwiched in between the permanentsubstrate and the first conductivity type ohmic contact layer; andremoving the temporary substrate and the first bonding layer.

According to a preferred embodiment of the present invention, the secondbonding layer is composed of a second adhesive layer, and a material ofthe second adhesive layer is preferably PbSn, AuGe, AuBe, AuSn, Sn, Inor PdIn. According to another preferred embodiment of the presentinvention, a material of the permanent substrate is preferably Si, Ge,SiC, AlN, Cu or Al for electrical conduction.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention are more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 through FIG. 8 are schematic flow diagrams showing the processfor manufacturing a high efficiency light-emitting diode in accordancewith a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses a high efficiency light-emitting diodeand a method for manufacturing the same, which can enhance thebrightness of the light-emitting diode and can increase the operationreliability and stability of the light-emitting diode. In order to makethe illustration of the present invention more explicit, the followingdescription is stated with reference to FIG. 1 through FIG. 8.

FIG. 1 through FIG. 8 are schematic flow diagrams showing the highefficiency light-emitting diode manufacturing process in accordance witha preferred embodiment of the present invention. In an exemplaryembodiment of the present invention, in the fabrication of alight-emitting diode device, a growth substrate 100 is provided, and anetching stop layer 152 is directly grown on a surface of the growthsubstrate 100 by, for example, a deposition method. A first conductivitytype ohmic contact layer 126 is formed on the etching stop layer 152,wherein a material of the first conductivity type ohmic contact layer126 may be GaAs, GaAsP or AlGaInP. An illuminant epitaxial structure 110is grown on the first conductivity type ohmic contact layer 126 by, forexample, a metal organic chemical vapor deposition (MOCVD) method, aliquid phase deposition (LPD) method or a molecular beam epitaxy (MBE)method. In one embodiment, the illuminant epitaxial structure 110comprises a first conductivity type cladding layer 102, an active layer104, a second conductivity type cladding layer 106 and a transparentcurrent-spreading layer 108 grown and stacked on a surface of the firstconductivity type ohmic contact layer 126 in sequence, such as shown inFIG. 1. The illuminant epitaxial structure 110 has a surface 112 and asurface 114 on two opposite sides, wherein the surface 112 of theilluminant epitaxial structure 110 is directly connected with thesurface of the first conductivity type ohmic contact layer 126, and thesurface 114 of the illuminant epitaxial structure 110 is exposed. In theinvention, the first conductivity type and the second conductivity typeare different conductivity types. In the present exemplary embodiment,the first conductivity type is N-type, and the second conductivity typeis P-type to produce a P-side up light-emitting diode structure. Amaterial of the growth substrate 100 is preferably a group III-Vcompound semiconductor material, such as GaAs, InP, GaP or sapphire. Amaterial of the first conductivity type cladding layer 102 may beAl_(x)Ga_(1-x)As (x>0.4) or (Al_(x)Ga_(1-x))_(y)In_(1-y)P (x>0.4). Amaterial of the second conductivity type cladding layer 106 may beAl_(x)Ga_(1-x)As (x>0.4) or (Al_(x)Ga_(1-x))_(y)In_(1-y)P (x>0.4). Amaterial of the active layer 104 may be (Al_(x)Ga_(1-x))_(y)In_(1-y)P(x<0.5). A material of the transparent current-spreading layer 108 maybe GaP, GaAsP, AlGaAs or AlGaInP.

After the formation of the illuminant epitaxial structure 110 iscompleted, a second conductivity type compound electrode pad 120 isformed on a portion region of the surface 114 of the illuminantepitaxial structure 110 for the light-emitting diode to electricallyconnected to an outer circuit. In the present exemplary embodiment, thesecond conductivity type compound electrode pad 120 comprises an ohmiccontact metal layer 116 and a bonding metal pad 118 stacked on thesurface 114 of the illuminant epitaxial structure 110 in sequence, suchas shown in FIG. 2. A material of the ohmic contact metal layer 116 maybe AuBe, AuZn or CrAu. A material of the bonding metal pad 118 may be Auor Al.

Next, a temporary substrate 124 is bonded to the illuminant epitaxialstructure 110 and the second conductivity type compound electrode pad120 by using a bonding layer 122. After bonding, the bonding layer 122is sandwiched between the temporary substrate 124 and the surface 114 ofthe illuminant epitaxial structure 110, such as shown in FIG. 3. In thebonding step of the temporary substrate 124, the bonding layer 122 isfirst coated on the exposed portion of the surface 114 of the illuminantepitaxial structure 110 and the second conductivity type compoundelectrode pad 120, and then the temporary substrate 124 is adhered tothe bonding layer 122. In another embodiment, in the bonding step of thetemporary substrate 124, the bonding layer 122 is first coated on asurface of the temporary substrate 124, and then the bonding layer 122is adhered to the surface 114 of the illuminant epitaxial structure 110and the second conductivity type compound electrode pad 120 to completethe bonding of the temporary substrate 124 and the illuminant epitaxialstructure 110. When the temporary substrate 124 is bonded, the bondingtemperature is preferably controlled between about 150° C. and about500° C. The bonding layer 122 preferably comprises a protection layer146, a protection layer 150 and an adhesive layer 148, wherein theadhesive layer 148 is sandwiched between the protection layer 146 andthe protection layer 150, and the protection layer 150 is locatedbetween the protection layer 146 and the temporary substrate 124.Materials of the protection layer 146 and the protection layer 150 maybe SiO₂, Si₃N₄, Ni, Cr, spin on glass (SOG) coating photoresist, Al₂O₃,MgO or ZnO. A material of the adhesive layer 148 may be PbSn, AuGe,AuBe, AuSn, Sn, In, PdIn, BCB, epoxy, Si, PI or spin on glass coatingpolymer. The temporary substrate 124 is preferably composed of an easilyfabricate, low cost material and is different from that of a permanentsubstrate 138 (referring to FIG. 6), such as glass, Si, GaAs, Cu or Al.

Then, the growth substrate 100 is removed to expose the etching stoplayer 152 by, for example, a chemical etching method or a polishingmethod. The etching stop layer 152 is removed to expose the firstconductivity type ohmic contact layer 126 by, for example, a chemicaletching method or a polishing method. Next, the first conductivity typeohmic contact layer 126 is patterned to expose a portion of the surface112 of the illuminant epitaxial structure 110. A first conductivity typeohmic contact metal layer 128 is formed to stack on the firstconductivity type ohmic contact layer 126 to improve the electricalquality of the light-emitting diode. A material of the firstconductivity type ohmic contact metal layer 128 may be a compoundmaterial, such as AuGe/Au, Au/AuGe/Au or AuGe/Ni/Au. A transparentconductive oxide layer 130 is formed to cover the first conductivitytype ohmic contact layer 126, the first conductivity type ohmic contactmetal layer 128 and the exposed portion of the surface 112 of theilluminant epitaxial structure 110. A material of the transparentconductive oxide layer 130 may be In₂O₃, SnO₂, ZnO, ITO, CTO, CuAlO₂,CuGaO₂ or SrCu₂O₂. Then, such as shown in FIG. 4, a reflective metallayer 132 is formed to cover the transparent conductive oxide layer 130to reflect the light emitted by the active layer 106 towards thereflective metal layer 132. A material of the reflective metal layer 132may be Au, Al, Ag, Cr or Ni. The reflective metal layer 132, thetransparent conductive oxide layer 130, the first conductivity typeohmic contact layer 126 and the first conductivity type ohmic contactmetal layer 128 comprise a reflective contact structure. Then, thereflective metal layer 132 may be directly bonded with a permanentsubstrate 138; or other additional processes of the illuminant epitaxialstructure 110 and the permanent substrate 138 may be selectivelyperformed, and then the bonding process of the illuminant epitaxialstructure 110 and the permanent substrate 138 is performed.

In the present exemplary embodiment, additional processes are performedfirst on the illuminant epitaxial structure 110 and the permanentsubstrate 138, and then the bonding process of the illuminant epitaxialstructure 110 and the permanent substrate 138 is performed. Referring toFIG. 5, after the reflective metal layer 132 is formed, a diffusionbarrier layer 134 is formed to cover the reflective metal layer 132. Amaterial of the diffusion barrier layer 134 may be Mo, Pt, W, ITO, ZnOor MnO.

In the meanwhile, the permanent substrate 138 is provided, wherein amaterial of the permanent substrate 138 may be Si, Ge, SiC, AlN, Cu, Alor sapphire. Selectively, a contact metal layer 136 and a contact metallayer 140 are respectively formed on opposite surfaces of the permanentsubstrate 138 to improve the electrical contact quality. In the presentexemplary embodiment, when the permanent substrate 138 is bonded, abonding layer 142 is firstly coated on the contact metal layer 140 onthe permanent substrate 138, such as shown in FIG. 6, and then thebonding layer 142 is adhered to the diffusion barrier layer 134 underthe surface 112 of the illuminant epitaxial structure 110 to completethe bonding of the permanent substrate 138 and the illuminant epitaxialstructure 110, such as shown in FIG. 7. In another embodiment, when thepermanent substrate 138 is bonded, the bonding layer 142 may be firstlycoated on the diffusion barrier layer 134 under the surface 112 of theilluminant epitaxial structure 110, and then the contact metal layer 140on the permanent substrate 138 is adhered to the bonding layer 142 tosuccessfully complete the bonding of the permanent substrate 138 and theilluminant epitaxial structure 110. When the permanent substrate 138 isbonded, the bonding temperature is preferably controlled between about150° C. and about 500° C. The bonding layer 142 preferably comprises anadhesive layer, and a material of the adhesive layer may be PbSn, AuGe,AuBe, AuSn, Sn, In, PdIn or Si.

After the bonding of the permanent substrate 138 and the illuminantepitaxial structure 110, the temporary substrate 124 and the bondinglayer 122 are removed by an etching method, such as a chemical etchingmethod, to expose the surface 114 of the illuminant epitaxial structure110 and the second conductivity type compound electrode pad 120, so asto complete the fabrication of a light-emitting diode 144, such as shownin FIG. 8.

According to the aforementioned description, there is no hightemperature process being performed after the bonding of an illuminantepitaxial structure and a permanent substrate in an exemplary embodimentof the present invention, so that the selectiveness of the bondingmaterial is increased, thereby providing easier process conditions,broadening the process window of the bonding process and effectivelyenhancing the reliability of the light-emitting diode.

According to the aforementioned description, the high efficiencylight-emitting diode in an exemplary embodiment of the present inventionhas a P-side up illuminant epitaxial structure, so that a transparentcurrent-spreading layer having a larger thickness and higher electricalconductivity can be epitaxially grown. Therefore, light extractionefficiency of the light-emitting diode is increased, thecurrent-spreading effect is improved, and the area of the opaqueelectrodes is decreased, thereby enhancing brightness of thelight-emitting diode.

According to the aforementioned description, because silicon may beadopted as a material of a permanent substrate in an exemplaryembodiment of the present invention, and silicon has properties of highthermal conductivity, high electrical conductivity, being easilyprocessed, and superior reliability operated under large current,operation performance of the light-emitting diode is effectivelyenhanced.

As is understood by a person skilled in the art, the foregoing preferredembodiments of the present invention are illustrated of the presentinvention rather than limiting of the present invention. It is intendedto cover various modifications and similar arrangements included withinthe spirit and scope of the appended claims, the scope of which shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar structure.

What is claimed is:
 1. A method for manufacturing a high efficiencylight-emitting diode, comprising: providing a growth substrate; forminga first conductivity type ohmic contact layer on the growth substrate;forming an illuminant epitaxial structure on the first conductivity typeohmic contact layer; forming a first electrode pad on the illuminantepitaxial structure; providing a temporary substrate; bonding thetemporary substrate to the illuminant epitaxial structure and the firstelectrode pad; removing the growth substrate; forming a second ohmiccontact metal layer on the side of the illuminant epitaxial structureopposite to the temporary substrate; forming a reflective metal layer onthe second ohmic contact metal layer; providing a permanent substrate;bonding the permanent substrate to the reflective metal layer; andremoving the temporary substrate, further comprising patterning thefirst conductivity type ohmic contact layer to expose a potion of theilluminant epitaxial structure.
 2. The method for manufacturing a highefficiency light-emitting diode according to claim 1, wherein theilluminant epitaxial structure comprises a first conductivity typecladding layer, an active layer, a second conductivity type claddinglayer and a transparent current-spreading layer.
 3. The method formanufacturing a high efficiency light-emitting diode according to claim1, wherein the first electrode pad comprises a first ohmic contact metallayer and a bonding metal pad stacked on the illuminant epitaxialstructure in sequence.
 4. The method for manufacturing a high efficiencylight-emitting diode according to claim 3, wherein the first ohmiccontact metal layer is selected from the group consisting of AuBe, AuZnand CrAu.
 5. The method for manufacturing a high efficiencylight-emitting diode according to claim 1, wherein the second ohmiccontact metal layer is a compound material selected from the groupconsisting of AuGe/Au, Au/AuGe/Au and AuGe/Ni/Au.
 6. The method formanufacturing a high efficiency light-emitting diode according to claim1, wherein the reflective metal layer is selected from the groupconsisting of Au, Al, Ag, Cr and Ni.
 7. The method for manufacturing ahigh efficiency light-emitting diode according to claim 1, wherein thestep of bonding the temporary substrate comprises coating a firstbonding layer on the illuminant epitaxial structure and the firstelectrode pad, and then adhering the temporary substrate to the firstbonding layer.
 8. The method for manufacturing a high efficiencylight-emitting diode according to claim 1, wherein a bonding temperatureof bonding the temporary substrate is between about 150° C. and about500° C.
 9. The method for manufacturing a high efficiency light-emittingdiode according to claim 1, between the step of providing the growthsubstrate and the step of forming the illuminant epitaxial structure,further comprising forming an etching stop layer on the growthsubstrate.
 10. The method for manufacturing a high efficiencylight-emitting diode according to claim 1, between the step of formingthe second ohmic contact metal layer on the illuminant epitaxialstructure and the step of forming the reflective metal layer on thesecond ohmic contact layer, further comprising forming a transparentconductive oxide layer on the second ohmic contact metal layer; whereinthe transparent conductive oxide layer is selected from the groupconsisting of In₂O₃, SnO₂, ZnO, ITO, CTO, CuAlO₂, CuGaO₂ and SrCu₂O₂.11. The method for manufacturing a high efficiency light-emitting diodeaccording to claim 1, between the step of forming the reflective metallayer and the step of providing the permanent substrate, furthercomprising forming a diffusion barrier layer to cover the reflectivemetal layer.
 12. The method for manufacturing a high efficiencylight-emitting diode according to claim 11, wherein the diffusionbarrier layer is selected from the group consisting of Mo, Pt, W, ITO,ZnO, and MnO.
 13. The method for manufacturing a high efficiencylight-emitting diode according to claim 1, between the step of providingthe permanent substrate and the step of bonding the permanent substrate,further comprising forming a first contact metal layer and a secondcontact metal layer to respectively cover two opposite surfaces of thepermanent substrate, and forming a second bonding layer on the permanentsubstrate or on the reflective metal layer, wherein the first contactmetal layer is located between the permanent substrate and the secondbonding layer.
 14. The method for manufacturing a high efficiencylight-emitting diode according to claim 1, between the step of removingthe growth substrate and the step of forming a second ohmic contactmetal layer on the side of the illuminant epitaxial structure oppositeto the temporary substrate, the step of patterning the firstconductivity type ohmic contact layer to expose a portion of theilluminant epitaxial structure occurs.
 15. The method for manufacturinga high efficiency light-emitting diode according to claim 1, wherein thefirst conductivity type ohmic contact layer is selected from the groupconsisting of GaAs, GaAsP, and AlGaInP.
 16. The method for manufacturinga high efficiency light-emitting diode according to claim 1, wherein thegrowth substrate is selected from the group consisting of GaAs, InP,GaP, and sapphire.
 17. The method for manufacturing a high efficiencylight-emitting diode according to claim 1, wherein the permanentsubstrate is selected from the group consisting of Si, Ge, SiC, MN, Cu,Al, and sapphire.
 18. The method for manufacturing a high efficiencylight-emitting diode according to claim 1, wherein the second ohmiccontact metal layer comprises AuGe.